In gas turbine engines, air is compressed at an initial stage, then is heated in combustion chambers, and the hot gas so produced passes to a turbine that, driven by the hot gas, does work which may include rotating the air compressor.
In a typical industrial gas turbine engine a number of combustion chambers combust fuel and hot gas flowing from these combustion chambers is passed via respective transitions to respective entrances of the turbine. More specifically, a plurality of combustion chambers commonly are arranged radially about a longitudinal axis of the gas turbine engine, and likewise radially arranged transitions comprise outlet ends that converge to form an annular inflow of hot gas to the turbine entrance. Each transition has a generally tubular structure so as to present a walled structure defining and surrounding a hot gas path between a respective combustion chamber and a respective entrance of the turbine.
Whether a transition is found in such gas turbine engine configuration or another design, it is subject to relatively high temperatures from the combusted and combusting gases passing from the combustion chamber. Considering its position between other dynamic components, temperature cycling, and other factors, the transition also is subject to low cycle fatigue. This is recognized to be a major design consideration for component life cycle.
Transitions may be cooled by open or closed cooling using compressed air from the turbine compressor, by steam, or by other approaches. Various designs of channels are known for passage of cooling fluids in the wall of the transition. The interior surface of the transition also may be coated with a thermal barrier coating such as are known to those skilled in the art.
One example of a prior art approach to cooling a transition is exemplified in U.S. Pat. No. 4,719,748, issued Jan. 19, 1988 to Davis et al. A separate sleeve extending over a transition is configured so as to provide impingement jets formed by apertures in the sleeve, and the sleeve is configured to duct spent impingement air toward the combustor. The spent impingement air mixes with other air not used for impingement cooling, and can be used for combustion. It is stated that the distance between the impingement sleeve and the transition duct surface is varied to control the velocity of air cross-flow from spent impingement air in order to minimize pressure loss due to cross-flow.
Not only is the overall cooling of a transition of concern; a specific cooling approach for the more downstream region of a transition has been proposed. U.S. Pat. No. 3,652,181, issued Mar. 28, 1972 to Wilhelm, teaches cooling of the more downstream end of a transition by means of a surrounding sleeve which admits cooling fluid (compressed air) exteriorly into the sleeve. The cooling fluid enters through inlet holes distributed with respect to a surface of an upper transition wall, and passes laterally around the transition, flowing in both directions around the sides of the transition, to exit through holes that allow the cooling fluid to enter an interior hot gas path defined by the transition.
Other approaches include those described in U.S. Patent Publication No. 2001/0004835, published Jun. 28, 2001, U.S. Pat. No. 6,964,170, issued Nov. 15, 2005, U.S. Pat. No. 4,695,247, issued Sep. 22, 1987, and U.S. Pat. No. 5,528,904, issued Jun. 25, 1996. The latter two patents provide approaches that include a film cooling component to cooling a combustor or hot gas duct liner, respectively.
Notwithstanding these and other approaches to cool transitions, there remains a need to provide an approach for more effective cooling of transitions used for gas turbine engines.